The present invention relates to a connecting member used to integrally connect a plurality of members which are independent from one another and, more particularly, to a connecting member capable of visibly indicating the connection strength.
A connecting member having a rod shape, such as a screw or a bolt, and connecting means on its outer surface for connecting a plurality of members, is conventionally used to integrally connect a plurality of members which are independent from one another. The clamping torque of the connecting member must be sufficient so that, during use, the interconnection between it and the plural members does not loosen under vibration conditions and other factors. The connecting member must also be capable of being set to a predetermined limit value corresponding to the maximum torque which the connecting member can exert. Therefore, it is usually necessary to employ a special tool such as a torque wrench so as to obtain a reliable indication of the torque exerted upon the plurality of members interconnected to the connecting member.
There also exists the possibility that the value of the clamping torque may decrease over time due to the periodic frequent variations in load forces exerted upon the plurality of integrated members during use. Thus, one can never be assured that the proper torque which is initially set by a torque wrench, will remain constant over time. Because of this, the clamping torque of the connecting member must be inspected periodically by a special tool, such as a torque wrench.
Therefore, significant time and labor are involved with these periodic inspections. This is especially true when there are a number of connecting members (such as bolts which must be inspected periodically), and when looseness and/or breakage of even one such connecting member cannot be tolerated from a safety viewpoint (e.g., in railroad track maintenance work, and periodic checks and maintenance of automobiles).